Integrate GUI with CLAWS
This is far better than Lightning and Outlook on features, but slow and lacking on integration with mail. Drag'n Drop just is way more uncomfortable than context-menu "create task from this mail" or "Mail this task"
Claws is lightning fast and has Python-scripting - ideal match to get the best PIM ever. It should be easy to tightly integrate these programes into one through a Claws plugin, creating a PIM suite that beats both Thunderbird/Lightning and Outlook.
Join forces now, let those applications start up together and let them communicate with eachother by contextmenu and shortcuts :-)
(This is "Basic CLI Support" for the rest of us)